Small multi-layer chip capacitors are used in various electronic devices due to their high capacity, high reliability and compact size. Along with demands for continuing reductions in size and improved reliability, there has been increasing demands for price reductions and increased capacity. Conventional approaches for the production of ceramic chip capacitors involve the application of a paste using conventional printing methods in alternating layers of dielectric and electrodes.
The electrodes incorporate metals or alloys. A sintering step can result in the oxidation of the metal unless the sintering of the layered structure is performed in a reducing atmosphere. However, sintering of the dielectric material in a reducing atmosphere can result in the reduction of the dielectric materials, which can lower the specific resistance and the corresponding capacitance of the structure. Specific types of dielectric material are selected to resist reduction during sintering in a reducing atmosphere. A desirable dielectric composition having desirable dielectric and stability properties include BaTiO3 as a main component along with optional additional metal/metalloid oxides as property modifiers.
In conventional chip capacitor processing, a plurality of chip capacitors is simultaneously printed as a periodic monolithic structure. The monolithic structure is cut to form the individual chip capacitors. To form the monolithic structure, layers are printed from a paste formed with an organic or aqueous dispersant. Various polymer binders, such as ethyl cellulose, polyvinyl butyral, and the like, generally are also used at low concentrations in forming the paste. The paste for formation of the dielectric material can include the desired metal oxides or other metal compositions that decompose into the metal oxides upon sintering. Similarly, the electrode paste can be formed from powders of the desired metals or alloys or metal compositions that convert to the metals or alloys upon sintering under reducing conditions. The layers are successively printed onto a polyethylene terephthalate (PET) polymer substrate or the like.
After printing the desired layers, the layered structure is then cut into desired shapes. The capacitors are pealed from the substrate before or after they are cut into individual units. The binder and dispersant are removed by heating at moderate temperatures in air. This moderate temperature is generally low enough that the inorganic particles are not significantly affected during this initial heating process. The structures are then sintered at a higher temperature under low oxygen partial pressures to complete the formation of a structure with alternating layers forming the capacitor. In particular, the electrode layers are formed as a uniform metallic layer with elemental metal or alloy, and the dielectric layers densify to form a compact capacitor structure.
Approaches have been developed for the production of highly uniform submicron and nanoscale particles by laser pyrolysis. Highly uniform particles are desirable for the fabrication of a variety of devices including, for example, batteries, polishing compositions, catalysts, and phosphors for optical displays. Laser pyrolysis involves an intense light beam that drives the chemical reaction of a reactant stream to form a flow of highly uniform particles following the rapid quench of the stream after leaving the light beam. Laser pyrolysis approaches have been adapted for the production of highly uniform coatings on substrate surfaces using an approach called light reactive deposition. Light reactive deposition can be used for the deposition of a variety of different compositions, by adapting reactant delivery techniques developed for laser pyrolysis. Light reactive deposition is suitable for the formation of multiple layers of different compositions.